Over the years, many portable exercising devices employing stretchable or tension cords have been developed. However, many of these devices are designed to exercise a particular muscle group and are not adapted to a full body workout. For instance, a device for exercising the muscle groups used for drawing and holding the draw of a bow is disclosed in U.S. Pat. No. 4,609,191. That device is designed solely to work out the muscles of a user's hand and arm.
Similarly, some devices are developed for specifically exercising a user's upper body muscles such as the devices disclosed in U.S. Pat. Nos. 4,540,173 and 3,807,730, while other devices are developed for specifically exercising one's lower body muscles such as the device disclosed in U.S. Pat. No. 3,531,113.
Some devices require the use of large, awkward and hard bars as disclosed in U.S. Pat. Nos. 4,059,265 and 4, 195,853. These devices can be heavy and difficult to manipulate.
While many exercise devices utilize stretchable cords to achieve the workout, they often do so in an inefficient or limiting manner. A device disclosed in U.S. Pat. No. 4,540,173 passes one tension cord twice through a flexible sheath. Much friction between the overlapping portions of the cord results from its use. This subjects the cord to greater wear and tear as it constantly rubs against itself, thereby reducing the durability and life of the device, and which provides only a single degree of resistance.